UNITED NATIONS (AP) — Australia and Britain on Wednesday pushed for engaging with Sri Lanka rather than isolating it, even as the United Nations warned it could launch a probe into suspected war crimes during the island’s civil conflict unless Sri Lanka conducts its own, proper investigation.

Western nations have been pressing Sri Lanka to account for thousands of civilians who are suspected to have died in the final months of the quarter-century war that ended in 2009 when government forces crushed resistance by Tamil rebels who were fighting for an ethnic homeland.

U.N. High Commissioner for Human Rights Navi Pillay. Pic: AP.

In a report issued in Geneva on Wednesday, U.N. High Commissioner for Human Rights Navi Pillay said she has seen no new or comprehensive Sri Lankan effort to properly and independently investigate the allegations of war crimes and other abuses during the civil conflict.

The U.N.’s 47-nation Human Rights Council has repeatedly demanded such an investigation, and Pillay said she would recommend that the council establish its own probe if Sri Lanka does not show more “credible” progress by March.

In his address to the U.N. General Assembly in New York on Tuesday, President Mahinda Rajapaksa complained of a “growing trend” of interference in the internal matters of developing countries on the pretext of security and human rights. He said recent provincial elections in the north of Sri Lanka — won by a Tamil party — had been crucial in promoting political empowerment and reconciliation.

(READ MORE: A look at the human rights situation in Sri Lanka)

While Sri Lanka has enjoyed peace in the past four years, rights groups have accused Rajapaksa of squelching dissent and suppressing the judiciary. After a recent visit to the South Asian island, Pillay said that democracy was being undermined and the rule of law eroded, with the country increasingly becoming an authoritarian state.

That set off an angry exchange.

The government claimed that Pillay had violated her mandate by making political statements. Sri Lanka’s defense secretary said her visit was influenced by propaganda from remnants of the Tamil Tiger rebels who lost the war. Pillay in turn accused Sri Lankan officials of waging a disinformation campaign against her.

At the United Nations in New York, where world leaders are gathered this week, Australia and Britain said Wednesday there remain important concerns about human rights and reconciliation in Sri Lanka, but also noted areas of progress. They encouraged countries to participate in the Commonwealth leaders’ meeting to be held in Sri Lanka in November. Human rights groups have urged a boycott.

“Sri Lanka will have an opportunity to show what progress has been made in areas of humanitarian support and human rights,” Australian Foreign Minister Julie Bishop told reporters. She said more could be achieved by engaging Sri Lanka than by isolating it.

Bishop welcomed this week’s provincial elections in a region that was ravaged by the war.

The provincial councils have little power, but the vote was seen as a step toward granting more autonomy for Tamils who have faced discrimination from the ethnic Sinhalese majority.